if your ps3 is on 3.41 then yea. if t is on 3.50 then yea. if your playing online right now then no. (3.55).
3.41- Buy a jailbreak off the internet
3.50- By a downgrade card (E3) and a jailbreak.
3.55- Downgradings patched so no luck.
To check you firmware go to System Settings then System Information and it will say it.
Actually yes, you can, and on any firmware. My friend figured out a way, he has got it to work with several different patches. Tutorial is on a different site though :/